On-line coupling of immunoaffinity-based solid-phase extraction and gas chromatography for the determination of s-triazines in aqueous samples.

The potential of immunoaffinity-based solid-phase extraction (IASPE) coupled on-line to gas chromatography (GC) for the determination of micropollutants was studied with emphasis on the interfacing of the immunoaffinity-based SPE and GC parts of the system. The cartridge containing the immobilized antibodies was coupled to the gas chromatograph via a reversed-phase cartridge (copolymer sorbent). After trace enrichment of the analytes on the immunoaffinity cartridge, they were desorbed and recollected on the reversed-phase cartridge by means of an acidic buffer. After clean-up and drying with nitrogen, desorption and transfer to the GC was done with ethyl acetate via an on-column interface in the partially concurrent solvent evaporation mode. The antibodies used in the immunoaffinity cartridge were raised against atrazine; several s-triazines were used as test compounds. Triazines that were structurally similar to atrazine, showed quantitative recovery. As an application, immunoaffinity SPE-GC was used for the analysis of river and waste water and orange juice. The selectivity of the system was such that non-selective flame ionization detection (FID) could be used to detect the analytes of interest in these complex matrices. The detection limits for 10-ml water samples were 15-25 ng/l for FID and about 1.5 ng/l for the nitrogen-phosphorus detection. Copyright (C) 1999 Elsevier Science B.V

Determination of chlorophenoxy acid herbicides in water by in situ esterification followed by in-vial liquidBliquid extraction combined with large-volume on-column injection and gas chromatographyBmass spectrometry

A new approach for rapidly analysing chlorophenoxy acid herbicides in water is presented. The chlorinated acids are derivatised with dimethyl sulphate in the water sample itself (800 μl) and, next, the methyl esters are extracted with 800 μl of n-hexane. A 200-μl volume of the extract is injected into the GC-MS system. The miniaturisation of both the methylation and extraction steps could be implemented because of the use of large-volume on-column injection and mass spectrometric detection. The optimisation of the methylation reaction for the simultaneous determination of (3,6-dichloro-2- methoxy)benzoic acid, (2-methyl-4-chlorophenoxy)- and (2,4- dichlorophenoxy)acetic acids, (±)-2-(4-chloro-2-methylphenoxy)- and 2-(2,4- dichlorophenoxy)propanoic acids and 4-(4-chloro-2-methylphenoxy)- and 4-(2,4- dichlorophenoxy)butyric acids showed that tetrabutylammonium salts act as catalysts. Addition of sodium hydroxide was required to obtain quantitative reaction yields for 4-(4-chloro-2-methylphenoxy)- and 4-(2,4- dichlorophenoxy)butyric acids. The methylation-cum-extraction procedure takes only 3 min per sample for a batch of seven samples. Linear calibration plots were obtained for the complete procedure and the limits of detection were of 10-60 ng/l with a signal-to-noise ratio (S/N) of 6. Relative standard deviations ranged from 8 to 15% (n = 7) for analyte concentrations of 0.5 μg/l in surface water. (C) 2000 Elsevier Science B.V

Monofluorinated analogues of polycyclic aromatic hydrocarbons as internal standards for GC-MS in environmental analysis

In the gas chromatographic determination of polycyclic aromatic hydrocarbons (PAHs), internal standards (ISs) are frequently used in order to correct for losses and fluctuating experimental parameters. In this study eight monofluorinated PAHs (F-PAHs) are used to this end. Analysis was by means of large-volume injection-gas chromatography with mass spectrometric detection (LVI-GC-MS). Relevant experimental results and performance data are presented, and it is demonstrated that the use of at least one F-PAH as IS improves the repeatability dramatically. As a brief application, F-PAHs were used as ISs for the trace-level determination of PAHs in soil, after extraction by means of pressurized liquid extraction (PLE) and liquid partitioning (LP). The suitability of the approach was demonstrated with naphthalene and pyrene as test compounds.L. Ramos thanks the Spanish Ministerio de Educación y Cultura for giving financial support.Peer reviewe

J. Chromatogr. A

The potential and current limitations of comprehensive two- dimensional gas chromatography coupled to time-of-flight mass spectrometry (GCxGC-TOF-MS) for the analysis of very complex samples were studied with the separation of cigarette smoke as an example. Because of the large number of peaks in such a GCxGC chromatogram it was not possible to perform manual data processing. Instead, the GC-TOF-MS software was used to perform peak finding, deconvolution and library search in an automated fashion; this resulted in a peak table containing some 30 000 peaks. Mass spectral match factors were used to evaluate the library search results. The additional use of retention indices and information from second-dimension retention times can substantially improve the identification. The combined separation power of the GCxGC-TOF-MS system and the deconvolution algorithm provide a system with a most impressive separation power. (C) 2002 Elsevier Science B.V. All rights reserved

Fast temperature programming in gas chromatography using resistive heating

The features of a resistive-heated capillary column for fast temperature-programmed gas chromatography (GC) have been evaluated. Experiments were carried out using a commercial available EZ Flash GC, an assembly which can be used to upgrade existing gas chromatographs. The capillary column is placed inside a metal tube which can be heated, and cooled, much more rapidly than any conventional GC oven. The EZ Flash assembly can generate temperature ramps up to 1200 °/min and can be cooled down from 300 to 50 °C in 30 s. Samples were injected via a conventional split/splitless injector and transferred to the GC column. The combination of a short column (5 m x 0.25 mm i.d.), a high gas flow rate (up to 10 mL/min), and fast temperature programmes typically decreased analysis times from 30 min to about 2.5 min. Both the split and splitless injection mode could be used. With n-alkanes as test analytes, the standard deviations of the retention times with respect to the peak width were less than 15% (n = 7). First results on RSDs of peak areas of less than 3% for all but one n-alkane indicate that the technique can also be used for quantification. The combined use of a short GC column and fast temperature gradients does cause some loss of separation efficiency, but the approach is ideally suited for fast screening as illustrated for polycyclic aromatic hydrocarbons, organophosphorus pesticides, and triazine herbicides as test compounds. Total analysis times - which included injection, separation, and equilibration to initial conditions - were typically less than 3 min